In recent years, a radio communication system called RFID system attracts attention. This system includes a small radio communication medium including an IC chip and an antenna and a radio communication apparatus called RFID reader writer. The radio communication apparatus writes data on and reads data from the radio communication medium in a non-contact manner using a radio wave or an electromagnetic wave.
An RFID system including plural RFID reader writers performs carrier sense to prevent radio waves output from the respective RFID reader writers from interfering with one another. The RFID reader writers search for free channels before outputting radio waves. When free channels are detected, the RFID reader writers output radio waves using the channels. Such a carrier sense system is called LBT (Listen Before Talk) system.
JP-A-2007-067621 discloses an RFID reader writer that detects, when abnormality is sensed in communication with a radio communication medium, a free channel again after a predetermined transmission pause time elapses and resumes the communication with the radio communication medium using the detected free channel.
However, even if the RFID reader writer detects the free channel, when other RFID reader writers in adjacent communication areas use channels of frequencies extremely close to that of the free channel, a communication error may occur because of the influence of the other RFID reader writers.